Isotope-- An element with the same number of protons but a different number of neutrons.
- adamblackburn Oct 21, 2008 Diagram and explain the Geiger-Marsden gold foil experiment and outline its significance in the development of the atomic model. Diagram from www.britannica.com
The alpha particles showed much more deflection than what was expected and remarkably a very small proportion even appeared to have bounced backward from the gold foil.Rutherford described his reaction in his notes as “It was quite the most incredible event that has ever happened in my life.It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you” The Rutherford model postulates: ·Atom is mostly empty space ·Center of atom is very small, dense, positively charged nucleus ·Electrons circle the nucleus in stable (yet to be explained) orbits
You may already be familiar with Niels Bohr and his work stemming from experimental evidence indicating the existence of electron energy levels. In a similar manner there is evidence for atomic and nuclear energy levels. Outline the evidence for each. Recall Bohr’s ideas about electrons in atoms being found in different energy levels (recall from chemistry). Evidence has been provided that shows that the nucleus itself also has specific energy levels. When a radioactive nuclide decays, alpha particles produced have discrete energy levels (make sure you understand the meaning of the word “discrete”). This implies that the nucleus loses energy in specific amounts or chunks as it moves from one allowed energy state to another. EVIDENCE - alpha particles emitted by a nucleus have specific amounts of energy For example: When Ra-226 decays to Rn-222
Ra-226 can decay by emitting an alpha particle
A simple atomic model (electrons in orbit around a nucleus) has a number of weaknesses that are not mentioned when the model is explained in earlier courses. Briefly outline two of these limitations.
The electrons undergo ionization. This gives them an electric charge, which means they can be deflected by an electromagnet in the Deflection stage. Depending on the strength of the electromagnet and the mass and charge of the atom, the electrons hit the detector in different locations. A substance is inserted into the mass spectrometer, gasified, and then pushed through the ionization phase, which gives the electrons a charge. They are then accelerated. After that, the electrons are pushed through the deflection chamber, which has an electromagnetic field that deflects the ions a certain amount depending on their charge and on their mass. The detector at the end determines where the electrons hit, and that information can be used to calculate the particles in a substance. - adamblackburn Oct 21, 2008
Nice summary of basic nuclear physics and atomic structure
For some detailed supplemental information check out DJY 2008 Topic 7 - Student Packet - supplemental.doc (added 28/10)
Provide a definition for the following terms
- Mass (nucleon) number -- the number of protons plus neutrons.
- Atomic (proton) number -- the number of protons in the atom. Defines what element the atom is.
- Nuclide -- an element defined by the number of protons, neutrons, and energy content (I think? http://en.wikipedia.org/wiki/Nuclide)
- Nucleon-- Either a proton or a neutron.
- Isotope-- An element with the same number of protons but a different number of neutrons.
-Diagram and explain the Geiger-Marsden gold foil experiment and outline its significance in the development of the atomic model. Diagram from www.britannica.com
The alpha particles showed much more deflection than what was expected and remarkably a very small proportion even appeared to have bounced backward from the gold foil. Rutherford described his reaction in his notes as “It was quite the most incredible event that has ever happened in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you”
The Rutherford model postulates:
· Atom is mostly empty space
· Center of atom is very small, dense, positively charged nucleus
· Electrons circle the nucleus in stable (yet to be explained) orbits
You may already be familiar with Niels Bohr and his work stemming from experimental evidence indicating the existence of electron energy levels. In a similar manner there is evidence for atomic and nuclear energy levels. Outline the evidence for each.
Recall Bohr’s ideas about electrons in atoms being found in different energy levels (recall from chemistry). Evidence has been provided that shows that the nucleus itself also has specific energy levels.
When a radioactive nuclide decays, alpha particles produced have discrete energy levels (make sure you understand the meaning of the word “discrete”). This implies that the nucleus loses energy in specific amounts or chunks as it moves from one allowed energy state to another. EVIDENCE - alpha particles emitted by a nucleus have specific amounts of energy
Ra-226 can decay by emitting an alpha particle
A simple atomic model (electrons in orbit around a nucleus) has a number of weaknesses that are not mentioned when the model is explained in earlier courses. Briefly outline two of these limitations.
Mass spectrometer
The electrons undergo ionization. This gives them an electric charge, which means they can be deflected by an electromagnet in the Deflection stage. Depending on the strength of the electromagnet and the mass and charge of the atom, the electrons hit the detector in different locations. A substance is inserted into the mass spectrometer, gasified, and then pushed through the ionization phase, which gives the electrons a charge. They are then accelerated. After that, the electrons are pushed through the deflection chamber, which has an electromagnetic field that deflects the ions a certain amount depending on their charge and on their mass. The detector at the end determines where the electrons hit, and that information can be used to calculate the particles in a substance. -